A fixture drain with a 2-inch trap must have a minimum diameter of which of the following?

When assessing the minimum diameter for a fixture drain with a 2-inch trap, it is essential to understand plumbing standards and requirements. A trap's function is to prevent sewer gases from entering the living space while allowing wastewater to flow freely. The size of the fixture drain must accommodate the flow produced by the trap without causing blockages or improper drainage.

A 2-inch trap typically serves a fixture with a significant flow of wastewater, such as a sink or a shower. According to plumbing codes, the minimum diameter of the fixture drain piping should generally be at least the same size as the trap to ensure proper drainage. However, it is common practice and advised to have a slightly larger minimum size to accommodate the flow and prevent back-pressure in the system.

Choosing a minimum diameter of 1 1/2 inches allows for adequate capacity to handle the waste from the 2-inch trap while still being compliant with plumbing standards. This size helps ensure that the system runs efficiently and reduces the risk of clogs or other issues that can arise from using a diameter that is too small.

Thus, a minimum drain diameter of 1 1/2 inches is the correct choice when dealing with a fixture drain associated with a 2-inch trap.